what's the relation between registerSecret and "Sprites and State Channels"

[nkbai]

this paper https://arxiv.org/abs/1702.05812

https://github.com/raiden-network/raiden/tree/master/raiden/smart_contracts vs https://github.com/raiden-network/raiden-contracts

The first contract to compare expiration using the current blockchain, and the second contract to compare using the SecretRegistry.

what's function of SecretRegistry? Record the time when the password first appeared?
thanks